Source: http://www.abarim-publications.com/Dictionary/si/si-b-l.html

שבל

שבל

The root שבל (sbl) occurs all over the Semitic language spectrum, but since it's not used as verb in the Bible, it's not clear what it may have meant in Hebrew. Judging from the derivatives, the central meaning of this root is probably something like going forth:

The feminine noun שבלת (shibboleth) denoting a flowing stream (Judges 12:6, Psalm 69:2 and 69:15, and Isaiah 27:12 only). This or the next word was used by the men of Gilead to identify men of Ephraim (Judges 12:6).

The identical feminine noun שבלת (shibbolet), meaning ears of grain (Job 24:24). The masculine version שבלים (shibbelim) occurs in Genesis 41:5-27, Ruth 2:2 and Isaiah 17:5. Other verbs that mean flow also yield nouns that have to do with produce. Produce was probably seen as "flowing" from the land.